Performance and efficiency of an engine may be improved by combining a central throttle with port throttles. The central throttle regulates air flow into a plurality of cylinders while each port throttle regulates air flow into a single cylinder. In one example, a central throttle may be positioned in an engine air intake system upstream of an engine air intake manifold that routes air from the central throttle to engine cylinders. Intake manifold runners direct air from the intake manifold to cylinder intake ports. A port throttle positioned within each cylinder intake port, or alternatively within each intake manifold runner, regulates air flow into an individual engine cylinder. However, cylinder charge maldistribution between engine cylinders may occur at lower engine loads when a central throttle is combined with port throttles.
Central and port throttles may also be combined with a turbocharger to improve engine output torque. However, turbocharger lag (e.g., delayed response time) may occur in systems with a central throttle and port throttles due to increased intake manifold filling time and/or throttle positioning that may enhance steady-state engine operation but that may also reduce transient engine performance.
The inventors herein have recognized the above-mentioned limitations and have developed an engine operating method, comprising: operating an engine with a central throttle and a plurality of port throttles; and increasing a port throttle opening amount and decreasing a central throttle opening amount in response to a flow distribution difference between the plurality of port throttles greater than a threshold flow distribution difference and engine air flow less than a threshold air flow. Further, in one example, the inventors adjust the central throttle and the port throttle such that a greater pressure drop occurs across the port throttle than the central throttle in response to turbine speed less than a threshold.
By increasing a port throttle opening amount and decreasing a central throttle opening amount, it may be possible to improve charge distribution between engine cylinders. In particular, use of port throttles to regulate cylinder air flow can be decreased during conditions when small changes in port throttle angle can have a large effect on cylinder charge. Instead, flow to the cylinder can be regulated via the central throttle. In this way, the possibility of cylinder maldistribution may be reduced. Additionally, the central throttle opening amount may be increased while the port throttle opening amount is decreased to allow the intake manifold to fill with air so that a turbocharger coupled to the engine spins up more rapidly when the port throttles are opened in response to an increased accelerator demand.
The present description may provide several advantages. Specifically, the approach may provide improved transient torque response time. Further, the approach may provide improved cylinder air-fuel control at lower engine loads, thereby improving engine emissions. Further still, portions of the approach may be applied to naturally aspirated engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.